In the newly released iTunes 10.6, Apple has quietly added the ability for users to select higher quality audio conversion bitrates when syncing to an iPhone, iPod or iPad.

Previously, users were given the option to down-convert higher bitrate songs to a low-end 128kbps. The smaller, lower-quality files allowed users to save space on their portable device and fit more music and files onto it.

But in earlier versions of iTunes, 128kbps was the only quality option for downgrading audio. Apple changed that last week with the release of iTunes 10.6, giving users two new options.

Now, with the latest version of iTunes, users can also choose to down-convert audio to quality levels of 192kbps or 256kbps, giving users a total of three bitrate options when syncing music to their mobile device.

Purchases from iTunes are encoded at 256kbps, but users who rip their own CDs might do so at a higher quality bitrate of 320kbps. The new setting would give them an option to slightly reduce the quality of those files to 256kbps when synced to a mobile device, while still retaining the higher quality 320kbps copy stored on their Mac or PC.

Music encoded as 256kbps AAC files first came to the iTunes Store in 2007 with the launch of Apple's iTunes Plus. That marked the debut of DRM-free music tracks encoded at a higher quality bitrate that Apple claims is virtually indistinguishable from the original recordings.

Earlier this year, legendary rock artist Neil Young indicated that he was working with Apple on producing a new super high-definition music format that would offer users uncompromised studio quality sound in the form of digital music downloads from iTunes. And in early 2011, there were also indications that Apple was interested in offering 24-bit music on iTunes, up from the current 16-bit quality.

And in February, one rumor claimed that Apple was working on a new audio file format to improve its iCloud service. The new file is rumored to improve the quality of streaming music to mobile devices like the iPhone, while also improving the quality to a high-definition copy when users have more bandwidth or storage available on their device.